Patent EP-1087226-A1 (EP)
Inventor: KON MASAO
IPC: G01N27/419
Filed: 2000-09-20
Abstract: It is an object of the present invention to provide an
improved gas analyzer capable of correctly monitoring the
concentration of a discharged NO x  even if an air ratio λ is less
than 1. It is another object of the present invention to provide
a gas analyzer calibrating method involving the use of the
improved gas analyzer. The gas analyzer of the present invention
comprises: a gas sensor (2,100) which includes a first diffusion rate
controlling passage (12), a first internal space (6) communicated with
the first diffusion rate controlling passage (12), a second diffusion
rate controlling passage (13), a second internal space (7) communicated
with the second diffusion rate controlling passage (13), a third
diffusion rate controlling passage (14), a third internal space (8)
communicated with the third diffusion rate controlling passage (14),
and an air introducing duct (31);
wherein the first internal space (6) is provided for effecting the
combustion of some combustible gases in the object gas, and is provided with a first
electro-chemical pump (4b,16,18) for adjusting an oxygen partial pressure
within the first internal space (6), so that the internal space
constantly contains a sufficient amount of oxygen capable of
effecting the combustion of the combustible gases contained in
the object gas which has been introduced into the internal space (6)
through the first diffusion rate controlling passage (12);
wherein the second internal space (7) is
provided with a second electro-chemical pump (4b,22,24) which is so
constructed that when an amount of oxygen is drawn from the second
internal space atmosphere consisting of the object gas introduced
into the second internal space (7) through the second diffusion rate
controlling passage (13), the oxygen partial pressure is decreased
to a sufficiently low value which does not reduce or decompose
the object gas and which is low enough for controlling the oxygen
partial pressure in the third internal space (8)
wherein the third internal space (8) is provided with
a third electro-chemical pump (4d,28,30) next to the third diffusion rate
controlling passage (14) and a fourth electro-chemical pump (4d,36,38) next to
the third electro-chemical pump (4d,28,30), the third electro-chemical pump (4d,28,30)
is so constructed that when the oxygen partial pressure of the
atmosphere within the second internal space (7) has a value which
will not substantially reduce or decompose the object gas, the
oxygen partial pressure is controlled to a further lower value
which does not bring about any significant influence to the
measurement of an amount of an object gas component, whereas the
fourth electro-chemical pump (4d,36,38) is provided to reduce or decompose
the object gas component introduced from the second internal
space (7) and to draw out an amount of oxygen generated at this moment;
wherein the air introducing duct (31) is provided in a manner such
that the outside pump electrodes (18,24) of the first and second
electro-chemical pumps are isolated so that these electrodes are
not directly exposed to the object gas and that this duct (31) can
serve as oxygen sources when oxygen is introduced into the first
internal space (6). The gas analyzer
calibrating method of the present invention involves the use of
the improved gas analyzer.